Why Pro Junglers often buy SightStone?

I know that sightstone is good on Lee Sin. It provides some good mobility for him and extra vision control.

But when watching Pro Jungler streamers or youtubers I sometimes see cases of them buying SightStone on Vi, Nunu, Elise even Jarvan.

I know that "Wards Win Games" and I believe in that, but is it worth it at all?

Solution 1:

The jungler has the ability to place wards all over the map. While warding the map is the job of every player, the jungler and supporter usually do more warding than the other roles.

High elo games usually have a lot more wards than mid-low elo ones. Everyone buys wards but the jungler has the advantage of not having to farm in lane which allows for offensive and defensive vision control without losing too much farm. Also the sightstone provides some extra HP which is useful on every jungler.

Solution 2:

Sightstone gives you free wards every time you go back, but also precious stats, especialy early in the game. An early sightstone on the jungler gives your team a huge vision advantage, and makes him tankier for a cheap cost.

The jungler also has more option for placing wards, since early on your support will probably be limited to botlane and the surounding jungle: if his team is winning, your jungler will place aggressive wards in the enemy jungle to be able to counter gank and snowball even further ahead. when your team is losing, he will ward his own jungle to allow his team to come and help him when the enemy jungler is invading, thus allowing the team to get back into the game.

You'll notice that in pro games and most high elo games, it's usual for the junglers, and even most laners, to buy 2-3 wards on each back, to assure vision for their team. Buying a sightstone on the jungler allows him to keep doing so, while not delaying his items too much, since junglers are usually starved on farm later in the game.